Electronics manufacturers are currently researching and developing future generations of electronic devices. One such development includes technology designed to surpass current CMOS (complementary metal oxide semiconductor) transistor technology as CMOS feature size approaches fundamental physical limits. Electronics, in particular CMOS devices, are based on the movement of electric charge. A next generation of electronic devices will focus on the interaction between electron spin and electron charge and on the interaction between multiple electron spins.
The physics behind spin electronics, or “spintronics,” dates to the early 20th century when experiments directed to the fine structure of hydrogen and alkali metals exhibited features inconsistent with prevailing scientific models. To explain the results, scientists proposed that an electron has an intrinsic angular momentum and magnetic dipole moment. The z components thereof are specified by a fourth quantum number ms that can assume a value of +½ or−½. The electron has an “up” spin or a “down” sp for a positive and negative quantum number ms respectively.
Devices that exploit spin properties, in lieu of or addition to charge degrees of freedom, offer potential benefits over devices operating on charge motion alone. One potential benefit of spintronics is reduced power consumption versus conventional electronics as the amount of energy required to change the orientation of an electron spin is much less than to move charge. This determines the ratio of the spin relaxation rate and switching rate and can amount to orders of magnitude. Another potential benefit is the ability to manufacture devices, for example memory cells and logic gates, that operate on a single atomic scale. The possibility of devices that combine reduced power consumption and atomic scale may fuel Moore's Law progress far beyond what is possible with, for example, CMOS technology.
The most significant commercial application of spintronics thus far is a ferromagnetic storage device (e.g., hard drive in a personal computer) and corresponding read-head. Based on the effect of giant-magnetoresistance (“GMR”), the storage device incorporates alternating layers of ferromagnetic and insulating material configured in such a manner that the resistance of the material is either small to large (and can indicate thereby a binary “0” or “1”) depending on the relative magnetic orientation in the ferromagnetic layers.
Spintronic applications, however, need not be limited to storage devices. In particular, semiconductor-based spin devices offer the potential to, through spin transport mechanisms like spin polarizers and spin valves, amplify signals. Amplifying spin devices may form the basis of logic gates and more sophisticated building blocks that eventually may lead to entire spin-based electronic systems.
Viewed as a whole, the spintronics paradigm offers a variety of potential improvements over, for example, CMOS. Those improvements include nonvolatility, high switching speed, high density, energy efficiency, and the ability to be customized and reconfigured.